%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Giuliani, Gaston
%A Pivin, M.
%A Fallick, A. E.
%A Ohnenstetter, D.
%A Song, Y.
%A Demaiffe, D.
%T Geochemical and oxygen isotope signatures of mantle corundum megacrysts from the Mbuji-Mayi kimberlite, Democratic Republic of Congo, and the Changle alkali basalt, China
%D 2015
%L fdi:010064156
%G ENG
%J Comptes Rendus Geoscience
%@ 1631-0713
%K Oxygen isotopes ; Chemistry ; Corundum ; Kimberlite ; Alkali basalt ; Origin ; Mantle
%K REPUBLIQUE DEMOCRATIQUE DU CONGO ; CHINE
%M ISI:000353428100004
%N 1
%P 24-34
%R 10.1016/j.crte.2014.12.003
%U https://www.documentation.ird.fr/hor/fdi:010064156
%> https://www.documentation.ird.fr/intranet/publi/2015/05/010064156.pdf
%V 347
%W Horizon (IRD)
%X Oxygen isotope signatures of ruby and sapphire megacrysts, combined with trace-element analysis, from the Mbuji-Mayi kimberlite, Democratic Republic of Congo, and the Changle alkali basalt, China, provide clues to specify their origin in the deep Earth. At Mbuji-Mayi, pink sapphires have 8180 values in the range 4.3 to 5.4 parts per thousand (N=10) with a mean of 4.9 +/- 0.4 parts per thousand, and rubies from 5.5 to 5.6 parts per thousand (N=3). The Ga/Mg ratio of pink sapphires is between 1.9 and 3.9, and in rubies, between 0.6 and 2.6. The blue or yellow sapphires from Changle have delta O-18 values from 4.6 to 5.2 parts per thousand, with a mean of 4.9 +/- 0.2 parts per thousand (N=9). The Ga/Mg ratio is between 5.7 and 11.3. The homogenous isotopic composition of ruby suggests a derivation from upper mantle xenoliths (garnet lherzolite, pyroxenite) or metagabbros and/or lower crustal garnet clinopyroxenite eclogite-type xenoliths included in kimberlites. Data from the pink sapphires from Mbuji-Mayi suggest a mantle origin, but different probable protoliths: either subducted oceanic protolith transformed into eclogite with delta O-18 values buffered to the mantle value, or clinopyroxenite protoliths in peridotite. The Changle sapphires have a mantle O-isotope signature. They probably formed in syenitic magmas produced by low degree partial melting of a spinel Iherzolite source. The kimberlite and the alkali basalt acted as gem conveyors from the upper mantle up to the surface.
%$ 064